Piping and Re-Direction

Piping Commands-pipe command is used to send the output of one command/program/process to another command/program/process for further processing. The Unix/Linux systems allow the standard output of a command to be connected as standard input of another command. We can make it do so by using the pipe character ‘|’.
e.g.
If we run this command
ls /usr/bin

Then it will give us a long listing of files of /usr/bin directory.

Now to view /usr/bin directory content properly we need to pipe the output of the above command to a program called “less”, which displays the output for us one screen at a time. So we can modify above written command as given below.
ls /usr/bin | less

Now to scroll the display one line at a time we can press Enter key. If we want to move forward one page, we can use the Space bar key and move backward one page by pressing b key. At the end of the file, we can press the q key to exit from the file.

Redirection (Input-Output Redirection)

By default, mostly all commands give output on the screen or take input from the keyboard. Linux however provides a way to send output to a file rather than sending on a computer screen similarly takes input from a file in place of the keyboard. this feature of sending the output to a file or getting input from a file is called redirection.
If we use a command
ls ./notes

Then this will display output of a list of files inside notes directory on the screen, but if we want to redirect its output to a file file.txt then we can use special symbol > sign as given below:
ls ./notes > file.txt

After redirecting output we can display file.txt content on screen using cat command

E.g. cat file.txt

Types of redirection

Output redirection ( > )
Input redirection ( < )

Output Redirection

Using this redirection, we can send the output of Linux command to a file. If the file already exists then it will be overwritten and if does not exist then a new file is created with the given file name. If we do not want a file to be overwritten, then we should use >> operator instead of > operator.